1. Field of the Invention
The invention relates to valves, and in particular to a valve for use in directing and controlling a high velocity stream of abrasive granular material. More particularly, the invention relates to a valve for a pressure-fed sandblaster having external shut-off means on the nozzle portion of the valve for controlling the spray of high velocity granular material.
2. Description of the Prior Art
The use of high pressure air for discharging a stream of an abrasive granular material for removing paint and rust from objects, such as car bodies, metal parts, building exteriors and the like, has been practiced for numerous years, much of which is commonly referred to as sandblasting. In this procedure, silica sand, glass beads or other granular materials are mixed with a stream of high pressure air and discharged through a nozzle which is held either manually or mechanically for directing the stream of the abrasive particles against the object being treated.
More recently, small portable pressure-fed blasters have been devised for smaller jobs than the heretofore large buildings, wherein a supply of compressed air is connected to a portable tank containing a predetermined amount of sand which is mixed with the pressure air stream. A manual valve is mounted on the end of a hose for turning on and shutting off the high velocity flow of granular material. A nozzle is incorporated in this valve for discharging the stream of abrasive particles and directing it against the object being cleaned with a sufficiently high velocity.
These valves use a manually operated ball-type shut-off mechanism in which a metal shut-off ball is mounted internally within the valve body and controlled by an external rotatable handle. This arrangement satisfactorily stops and starts the flow of abrasive material through the nozzle. However, problems arise in the use of such valves in that, when the valve is not rotated to a fully open or fully closed position, the abrasive material will continue to flow throughout the valve and out of the nozzle. The abrasive material, upon flowing in a somewhat irregular path through the partly opened or closed ball valve, quickly wears away or damages the metal ball valve and even the valve body. Thus, in a relatively short period of time, the ball or valve body is destroyed if operated in such a partly open or closed position, requiring replacement of the entire valve. These prior valves also require the use of both hands for their operation, one hand for holding the valve and the other hand for rotating the control lever.
An unsafe condition also is presented with these known manually operated hand-held valves since the valve remains open if dropped accidentally by a workman. The trailing hose and valve, due to the air pressure flowing therethrough, could whip about seriously injuring the operating or bystander or damaging equipment in the area since the valve remains in the open position until manually rotated to off position.
Therefore, these existing vaves provide both safety and maintenance problems and increased cost to the users thereof.
No valve construction for use with a high velocity stream of an abrasive granular material, of which I am aware, had eliminated the problems of repeated replacement and damage of the internal shut-off mechanism and the elimination of an unsafe condition if the valve is dropped during use, by a relatively simple external shut-off sealing member which returns automatically to a fully closed or shut-off position if not manually restrained in the open position.